In most radio systems, radio transmissions from individual user equipment must be synchronized when received by a node B. As user equipment may be located at various distances from the node B, the propagation delays of radio transmissions from different user equipment may vary. In order to compensate for the propagation delay, the user equipment advances its transmission time relative to its basis transmission schedule. This compensation may be achieved by a synchronization parameter such as a timing advance (TA) parameter. The node B calculates the value for the timing advance on the basis of the transmission received from the user equipment.
In packet-switched radio systems, as opposed to circuit-switched radio systems, the calculation of the timing advance is more difficult, as there is not necessarily a constant flow of traffic from the user equipment to the node B. Sometimes, signaling may be needed between the node B and the user equipment in order to restore the timing advance. In general, there is a need for a more flexible handling of the uplink synchronization parameter in modern packet-switched radio systems.